cleanup fasta token classes

pkg/compiler/lib/src/tree/nodes.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:collection' show IterableMixin;
 
 import 'package:front_end/src/fasta/fasta_codes.dart' show FastaMessage;
-import 'package:front_end/src/fasta/scanner.dart' show BeginGroupToken, Token;
+import 'package:front_end/src/fasta/scanner.dart' show Token;
 import 'package:front_end/src/fasta/scanner/token_constants.dart' as Tokens
     show PLUS_TOKEN;
 import 'package:front_end/src/fasta/scanner/characters.dart';
-import 'package:front_end/src/scanner/token.dart' show TokenType;
+import 'package:front_end/src/scanner/token.dart' show BeginToken, TokenType;
 
 import '../common.dart';
 import '../elements/elements.dart' show MetadataAnnotation;
 import '../util/util.dart';
 import 'dartstring.dart';
 import 'prettyprint.dart';
 import 'unparser.dart';
 
 abstract class Visitor<R> {
   const Visitor();
@@ skipping 1896 matching lines @@
     if (body != null) body.accept1(visitor, arg);
   }
 
   Token getBeginToken() => whileKeyword;
 
   Token getEndToken() => body.getEndToken();
 }
 
 class ParenthesizedExpression extends Expression {
   final Expression expression;
-  final BeginGroupToken beginToken;
+  final BeginToken beginToken;
 
   ParenthesizedExpression(
-      Expression this.expression, BeginGroupToken this.beginToken);
+      Expression this.expression, BeginToken this.beginToken);
 
   ParenthesizedExpression asParenthesizedExpression() => this;
 
   accept(Visitor visitor) => visitor.visitParenthesizedExpression(this);
 
   accept1(Visitor1 visitor, arg) {
     return visitor.visitParenthesizedExpression(this, arg);
   }
 
   visitChildren(Visitor visitor) {
@@ skipping 1340 matching lines @@
  */
 Object getTreeElement(TreeElementMixin node) => node._element;
 
 /**
  * Do not call this method directly.  Instead, use an instance of
  * TreeElements.
  */
 void setTreeElement(TreeElementMixin node, Object value) {
   node._element = value;
 }